Starting apparatus of passenger protecting apparatus and method thereof

ABSTRACT

A starting apparatus of a passenger protecting apparatus is actuated by detecting collision of a vehicle. The starting apparatus is provided so as to subtract a predetermined value from an acceleration signal fed from G sensor and integrate the subtracted acceleration signal, and forcedly set an integrated value to zero if the integrated value is less than zero. Further, the starting apparatus is provided so as to provide a starting signal when the integrated value exceeds a preset threshold value. Therefore, it is possible to discriminate collision to start the apparatus from other collision, prevent starting means from being unnecessarily actuated, and avoid malfunction of the starting means.

This application is a continuation of application Ser. No. 08/068,197,filed on May 28, 1993, now U.S. Pat. No. 5,440,485, the entire contentsof which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a starting apparatus of a passengerprotecting apparatus such as air bag or seat belt pretensioner, which isactuated by detecting collision of a vehicle.

2. Description of the Prior Art

FIG. 1 is a block diagram showing a conventional air bag startingcontrol unit which is disclosed in, for example, Japanese PatentApplication Publication No. 59-8574. In FIG. 1, reference numeral 1 isan acceleration sensor (hereafter abbreviated as G sensor), 155 is anintegrating circuit for integrating an acceleration signal output fromthe G sensor 1, and 156, 159 are comparator circuits for comparing anoutput from the integrating circuit 155 with starting prediction levelsV₁ and V₂. Further, reference numeral 157 is a time constant circuitincluding a diode D₂, a resistor R₂ and a capacitor C₂, and 158 is acomparator circuit for comparing an output from the time constantcircuit 157 with the output from the integrating circuit 155. Referencenumeral 160 is a reset pulse oscillator receiving an output from thecomparator 159 as an input, 161 is a differentiating circuit including acapacitor C₁ and a resistor R₁, and D₁ is a diode for supply an outputfrom the differentiating circuit 161 to an input terminal of theintegrating circuit 155.

A description will now be given of the operation of the prior artapparatus. At a time of collision of a vehicle, the G sensor 1 convertsacceleration into an electrical acceleration signal, and theacceleration signal is integrated and converted into a speed signal bythe integrating circuit 155. Typically, the integrating circuit 155 isreset for each predetermined cycle by an output signal from the pulseoscillator 160, and a starting signal is output if the output from theintegrating circuit 155 exceeds the starting prediction level of thecomparator circuit 158.

However, if the output from the integrating circuit 155 exceeds thestarting prediction level of the comparator circuit 159, the outputdrops so as to extend the cycle of the pulse oscillator 160, and passesthrough the differentiating circuit 161, resulting in an extended cycleof reset pulse for the integrating circuit 155.

Further, the output from the integrating circuit 155 varies the startingprediction level of the comparator circuit 158 through the comparatorcircuit 156 and the time constant circuit 157. In case the output fromthe integrating circuit 155 exceeds the starting prediction level, thecomparator circuit 158 outputs a starting signal so as to avoidmalfunction when receiving impact which has no need to start thestarting apparatus of the passenger protecting apparatus.

The starting apparatus of the passenger protecting apparatus in theprior art is provided as set forth above. Accordingly, there are somedrawbacks in that a circuit for generating a trigger is required toreset the integrating circuit within a predetermined period, and a timedelay generated by the trigger circuit causes another time delayrequired to generate the starting signal. Further, there is anotherdrawback in that the passenger protecting apparatus may be unnecessarilystarted by, for example, rough road travelling (i.e., travelling otherthan the collision such as running onto a curb) due to indistinctness ina difference between the rough road travelling and head-on collision ata low speed if the starting apparatus is started by only theacceleration signal at the time of the collision of the vehicle. Thereis still another disadvantage of difficulty of discriminating betweenthe head-on collision at the low speed (i.e., collision having no needto start the passenger protecting apparatus) and special collision(i.e., collision requiring starting of the passenger protectingapparatus) such as slipping under a rear deck of a truck.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a starting apparatus of a passenger protecting apparatus whichcan discriminate between acceleration applied due to conditions otherthan collision or low speed collision (i.e., collision having no need tostart the passenger protecting apparatus) and collision to start thepassenger protecting apparatus so as not to unnecessarily actuate thestarting apparatus, and thereby avoid malfunction of the startingapparatus.

It is another object of the present invention to provide a startingapparatus of a passenger protecting apparatus which can reduce acollision determining time so as to be less than that of a conventionalstarting apparatus.

It is still another object of the present invention to provided astarting apparatus of a passenger protecting apparatus which candetermine at the time of high speed collision more accurately than theconventional starting apparatus.

It is still another object of the present invention to provide astarting apparatus of a passenger protecting apparatus which can extractcharacteristics of acceleration signal waveforms of head-on collision ata low speed and head-on collision at a high speed so as to discriminatetherebetween.

It is still another object of the present invention to provide astarting apparatus of a passenger protecting apparatus which candiscriminate between rough road travelling and special collision withhigher reliability than that of the conventional starting apparatus.

It is still another object of the present invention to provide astarting apparatus of a passenger protecting apparatus which candiscriminate between the high speed collision and the rough roadtravelling and the special collision with respect to all conditionsrequiring a decision, such as collision or rough road travelling, withhigher reliability than that of the conventional starting apparatus.

According to the first aspect of the present invention, for achievingthe above-mentioned objects, there is provided a starting apparatus of apassenger protecting apparatus including a first collision determiningalgorithm unit for setting a speed signal to zero if the speed signalobtained by integrating an acceleration signal is less than zero whensequentially integrating after subtracting a constant value from theacceleration signal. The starting apparatus outputs a starting signaldepending upon an output from the first collision determining algorithmunit.

Consequently, in the starting apparatus of the passenger protectingapparatus according to the first aspect of the present invention, thefirst collision determining algorithm unit is provided to integrate withthe speed signal defined as zero if the speed signal obtained byintegrating after subtracting the constant value from the accelerationsignal is less than zero whereby it is possible to omit a triggercircuit for resetting of an integrating circuit, and reduce a collisiondetermining time.

According to the second aspect of the present invention, there isprovided a starting apparatus of a passenger protecting apparatusincluding a second collision determining algorithm unit having the firstcollision determining algorithm unit on the first stage for outputtingin response to an acceleration signal at the time of the low speedcollision, the first collision determining algorithm unit on the secondstage for outputting in response to the acceleration signal at the timeof the high speed collision, and an AND circuit obtaining the AND ofboth outputs from the respective first collision determining algorithmunits. Thus, the starting apparatus outputs a starting signal dependingupon the output from the second collision determining algorithm unit.

Consequently, in the starting apparatus of the starting apparatus of thepassenger protecting apparatus according to the second aspect, there isprovided the second collision determining algorithm unit having thefirst collision determining algorithm unit on the first stage, the firstcollision determining algorithm unit on the second stage for outputtingat the time of high speed collision, and the AND circuit obtaining theAND of both the outputs from the respective first collision determiningalgorithm units. Therefore, it is possible to further accuratelydetermine at the time of the high speed collision.

According to the third aspect of the present invention, there isprovided a starting apparatus of a passenger protecting apparatusincluding a third collision determining algorithm unit having a bandpass filter for extracting a particular frequency component from anacceleration signal so as to feed into the first collision determiningalgorithm unit. Thus, the starting apparatus outputs a starting signaldepending upon an output from the third collision determining algorithmunit.

Consequently, the starting apparatus of the passenger protectingapparatus according to the third aspect of the present invention isprovided with the third collision determining algorithm unit employingthe band pass filter on the preceding stage of the first collisiondetermining algorithm unit. Therefore, it is possible to extractcharacteristics of acceleration signal waveforms of head-on collision ata low speed and head-on collision at a high speed so as to discriminatetherebetween.

According to the fourth aspect of the present invention, there isprovided a starting apparatus of a passenger protecting apparatusincluding a fourth collision determining algorithm unit having apositive acceleration signal passing portion for inputting a positiveacceleration signal into the first collision determining algorithm uniton the first stage, and a negative acceleration signal inverting/passingportion for inputting a negative acceleration signal into the firstcollision determining algorithm unit on the second stage. Thus, thestarting apparatus outputs a starting signal depending upon an outputfrom the fourth collision determining algorithm unit.

Consequently, the starting apparatus of the passenger protectingapparatus according to the fourth aspect of the present invention isprovided with the fourth collision determining algorithm unit forcomparing an output of the integrated acceleration signal on thepositive side with an output of the integrated acceleration signal onthe negative side in the acceleration signals so as to define a morerapidly output as the starting signal. Therefore, it is possible todiscriminate the rough road travelling since an acceleration signalwaveform is also formed largely on the negative side at the time of therough road travelling.

According to the fifth aspect of the present invention, there isprovided a starting apparatus of a passenger protecting apparatusincluding a fifth collision determining algorithm unit having an ANDcircuit which obtains the AND of the output from the third collisiondetermining algorithm unit and the output from the fourth collisiondetermining algorithm unit. The starting apparatus outputs a startingsignal depending upon an output from the fifth collision determiningalgorithm unit.

Consequently, the starting apparatus of the passenger protectingapparatus according to the fifth aspect of the present invention isprovided with the fifth collision determining algorithm unit which is acombination of the third collision determining algorithm unit and thefourth collision determining algorithm unit. Therefore, it is possibleto perform a highly reliable discrimination between the rough roadtravelling and the special collision.

According to the sixth aspect of the present invention, there is astarting apparatus of a passenger protecting apparatus including a sixthcollision determining algorithm unit having an AND circuit which obtainsthe AND of the output from the first collision determining algorithmunit and the output from the fifth collision determining algorithm unit.The starting apparatus outputs a starting signal depending upon anoutput from the sixth collision determining algorithm unit.

Consequently, the starting apparatus of the passenger protectingapparatus according to the sixth aspect of the present invention isprovided with the sixth collision determining algorithm unit which is acombination of the first collision determining algorithm unit and thefifth collision determining algorithm unit. Therefore, it is possible toprovide a safety function, and perform a highly reliable discriminationbetween the rough road travelling and the special collision.

According to the seventh aspect of the present invention, there isprovided a starting apparatus of a passenger protecting apparatusincluding a seventh collision determining algorithm unit having an ANDcircuit which obtains the AND of the output from the first collisiondetermining algorithm unit and the output from the fourth collisiondetermining algorithm unit. Thus, the starting apparatus outputs astarting signal depending upon an output from the seventh collisiondetermining algorithm unit.

Consequently, the starting apparatus of the passenger protectingapparatus according to the seventh aspect of the present invention isprovided with the seventh collision determining algorithm unit which isa combination of the first collision determining algorithm unit and thefourth collision determining algorithm unit. Therefore, it is possibleto provide a safety function, and perform a highly reliablediscrimination of the rough road travelling.

According to the eighth aspect of the present invention, there isprovided a starting apparatus of a passenger protecting apparatusincluding an eighth collision determining algorithm unit having an ORcircuit which obtains the OR of the output from the second collisiondetermining algorithm unit and the output from the sixth collisiondetermining algorithm unit. Thus, the starting apparatus outputs astarting signal depending upon an output from the eighth collisiondetermining algorithm unit.

Consequently, the starting apparatus of the passenger protectingapparatus according to the eighth aspect of the present invention isprovided with the eighth collision determining algorithm unit which is acombination of the second collision determining algorithm unit and thesixth collision determining algorithm unit. Therefore, it is possible toperform a highly reliable discrimination between the high speedcollision and the rough road travelling and the special collision amongall the collisions.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawings are for purpose ofillustration only and are not intended as a definition of the limits ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a conventional starting apparatus of apassenger protecting apparatus;

FIG. 2 is a block diagram showing one embodiment of a starting apparatusof a passenger protecting apparatus according to the first aspect of thepresent invention;

FIG. 3 is a block diagram showing a microcomputer forming a firstcollision determining algorithm unit;

FIG. 4 is a flowchart illustrating the operation of the embodiment ofFIG. 2;

FIGS. 5(a) to (e) are each signal waveform diagrams at an operativetime;

FIGS. 6(a) to (c) are explanatory diagrams showing a comparison betweentwo cases with presence and absence of reset operation for resetting aspeed signal to zero;

FIG. 7 is a block diagram showing one embodiment of the startingapparatus of the passenger protecting apparatus according to the secondaspect of the present invention;

FIG. 8 is a flowchart illustrating the operation of the embodiment ofFIG. 7;

FIG. 9 is sub-flowcharts illustrating the operation of the embodiment ofFIG. 7;

FIG. 10 is a block diagram showing one embodiment of the startingapparatus of the passenger protecting apparatus according to the thirdaspect of the present invention;

FIG. 11 is a flowchart illustrating the operation of the embodiment ofFIG. 10;

FIGS. 12(a) to (c) are frequency spectrum diagrams of a band passfilter;

FIGS. 13(A) to (D) are signal waveform diagrams at the time of twodifferent collisions;

FIG. 14 is a block diagram showing one embodiment of the startingapparatus of the passenger protecting apparatus according to the fourthaspect of the present invention;

FIG. 15 is a flowchart illustrating the operation of the embodiment ofFIG. 14;

FIG. 16 is a block diagram showing one embodiment of the startingapparatus of the passenger protecting apparatus according to the fifthaspect of the present invention;

FIG. 17 is a flowchart illustrating the operation of the embodiment ofFIG. 16;

FIGS. 18(A)-(D) are signal waveform diagrams illustrating the operationof the embodiment of FIG. 16;

FIG. 19 is a block diagram showing one embodiment of the startingapparatus of the passenger protecting apparatus according to the sixthaspect of the present invention;

FIG. 20 is a flowchart illustrating the operation of the embodiment ofFIG. 19;

FIG. 21 is a flowchart illustrating the operation of the embodiment ofFIG. 19;

FIG. 22 is a block diagram illustrating one embodiment of the startingapparatus of the passenger protecting apparatus according to the seventhaspect of the present invention;

FIG. 23 is a flowchart illustrating the operation of the embodiment ofFIG. 22;

FIG. 24 is a block diagram showing one embodiment of the startingapparatus of the passenger protecting apparatus according to the eighthaspect of the present invention;

FIG. 25 is a flowchart illustrating the operation of the embodiment ofFIG. 24;

FIG. 26 is a block diagram showing a detailed configuration of acollision determining algorithm unit of FIG. 24; and

FIG. 27 is a flowchart illustrating the operation of the embodiment ofFIG. 26.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described in detailreferring to the accompanying drawings.

Embodiment 1

A description will now be given of the operation of one embodiment ofthe present invention with reference to the drawings. FIG. 2 is a blockdiagram showing the embodiment according to the first aspect of thepresent invention. In FIG. 2, reference numeral I is a first collisiondetermining algorithm unit including a subtraction processing portion 2afor subtracting a constant value g_(a) from an output of the G sensor 1,an integration processing portion 2b having a function for initializingto zero in case an integrated value F of the output from the subtractionprocessing portion 2a is less than zero, a comparison processing portion2c for comparing the integrated value F with preset voltage v_(a), andan on-timer 2d for holding an ON state for a predetermined period byreceiving an output from the comparison processing portion 2c. Referencenumeral 30 means a switching transistor which is conducted by receivingan output from the first collision determining algorithm unit I, andreference numeral 28 is starting means of the passenger protectingapparatus which is connected between the transistor 30 and a DC powersource 29, and is referred to as "squib".

FIG. 3 illustrates the first collision determining algorithm unit shownin FIG. 2, which is formed by a microcomputer including an input unit101, CPU 102, a memory 103, an output unit 104. Other components of FIG.3 are identical with those of FIG. 2, and the descriptions thereof areomitted.

Next, a description will now be given of the operation of the embodimentof FIG. 2 with reference to a flowchart shown in FIG. 4. In Step ST32, asampling time is input, and an acceleration signal having the amount ofoffset is input to go in Step ST33. After output of a starting signal isstopped in Step ST34, the acceleration signal B₋₁ preceding by onemoment, and the integrated value F are initialized to zero. Theacceleration signal output from the G sensor 1 is fetched, and theacceleration signal is defined as A in Step ST36. In Step ST37, theamount of offset g_(a) of the acceleration signal set in Step ST33 issubtracted from A so as to be defined as B. Subsequently, trapezoidalintegration of the acceleration signal is performed in Step ST38.

In Step ST39, the value B of the current acceleration signal is inputinto the value B₋₁ of the acceleration signal preceding by one moment soas to determine whether or not the integrated value F is less than zero.If F is less than zero, the operation proceeds in a direction of YES toset the integrated value F to zero in Step ST41, and the operationproceeds to Step ST42. Otherwise, if the integrated value F is greaterthan zero in Step ST40, the operation proceeds in a direction of NO,that is, to Step ST42. Further, if the integrated value F is less than apreset threshold value V_(TH) in Step ST42, the operation proceeds inthe direction of NO instead of outputting the starting signal. Thus, theoperation returns to Step ST36 so as to repeat the process as set forthabove.

On the other hand, if the integrated value F is greater than thethreshold value V_(TH) in Step ST42, it is determined that there occurscollision requiring the starting signal. Accordingly, the operationproceeds in the direction of YES so as to output the starting signal inStep ST43, and hold output of the starting signal for a predeterminedperiod in Step ST44, and the process is terminated in Step ST45.

A description will now be given of the process with reference towaveforms shown in FIG. 5.

In FIG. 5, (a) represents a waveform of an acceleration signal in casethere occurs collision at the time of travelling at a low speed (ofabout 10 km/h), which requires no starting signal. Further, (b)represents another waveform of an acceleration signal in case thereoccurs collision at the time of travelling at an intermediate or highspeed (of about 50 km/h), which requires the starting signal. In FIG. 5,the amount of offset g is a value set to be greater than theacceleration waveform (a).

Reference numerals (1) and (2) in (c) respectively mean waveforms whichare obtained by simply integrating the respective waveforms (a) and (b).A threshold value V_(VH1) at a time when the starting signal is outputis set to a value greater than that of the waveform (1). Further, a timeperiod required for the waveform (2) reaching the threshold valueV_(VH1) is defined as t_(A). Subsequently, the amount of offset g_(a) issubtracted from the waveform (a) so that the acceleration signal becomesa negative value. Similarly, the amount of offset g is subtracted fromthe waveform (b) to provide a waveform (d), and the waveform (d) isintegrated to provide a waveform (3) in (e).

On the other hand, if the amount of offset g is subtracted from thewaveform (a), the acceleration signal becomes a negative value.Accordingly, a threshold value V_(TH2) can be set to a considerablylower value than the threshold value V_(TH1). Further, a time periodt_(B) required for the waveform (3) in (e) reaching the threshold valueV_(TH2) is less than the determining time period t_(A) of (2) showingthe result of integration without subtracting the amount of offsetg_(a). As a result, it is possible to determine for a time period lessthan the determining time tA.

Next, the acceleration signal is integrated as shown in Steps ST40 andST41 of the flowchart of FIG. 4. With reference to FIG. 6, a descriptionwill now be given of a comparison between two cases with presence andabsence of a reset operation in which the integrated value of theacceleration signal, i.e., the speed signal F is set to zero if F isless than zero.

In FIG. 6, (a) represents a waveform of power supply voltage showingthat the DC power source 29 of FIG. 2 is turned ON at a time point to,and (b) is a waveform of the acceleration signal at the time of thecollision requiring the starting signal. Further, (c) is a waveformobtained by integrating after subtracting the amount of offset g_(a)from the waveform (b), wherein (1) represents a speed waveform in casethe reset operation for setting F to zero is not performed when F isless than zero, and (2) is a waveform in case the reset operation forsetting F to zero is performed when F is less than zero.

First, in case the reset operation for setting F to zero is notperformed when F is less than zero, it is necessary to forcedly input areset signal at a time period t_(d) in the speed waveform (1), resultingin requirement of trigger means. However, no trigger means is requiredin the waveform (2) wherein the reset operation for setting F to zero isperformed if F is less zero at a time point t_(e) when the accelerationsignal than zero.

Secondly, in Step ST41 of FIG. 4, F is clamped to becomes a negativevalue as shown by the waveform (2). Subsequently, the speed waveformrises from a time point when acceleration exceeds the amount of offsetg_(a). Thus, a time period t_(f) required for the waveform (2) reachingthe threshold value V_(TH) from a determination Starting time point isless than the time period t in the case of the waveform (1). As aresult, it is possible to obtain the starting signal for a reduceddetermining time period.

Embodiment 2

FIG. 7 is a block diagram showing one embodiment according to the secondaspect of the present invention. In FIG. 7, reference numeral II is asecond collision determining algorithm unit. The second collisiondetermining algorithm unit II includes a first collision determiningalgorithm unit IA on the first stage, a first collision determiningalgorithm unit IB on the second stage, and an AND circuit 6. The firstcollision determining algorithm unit IA on the first stage has the sameconfiguration as that of the first collision determining algorithm unitI shown in FIG. 2. The first collision determining algorithm unit IB onthe second stage includes a subtraction processing portion 3a forsubtracting a constant value g_(b) from an output from a G sensor 1, anintegration processing portion 3b for initializing an integrated value Fto zero if the integrated value F of an output from the subtractionprocessing portion 3a is less than zero, a comparison processing portion3c for comparing the integrated value F with preset voltage v_(b), andan on-timer 3d receiving an output from the comparison processingportion 3c so as to hold an ON state for a predetermined period. The ANDcircuit 6 obtains the AND of outputs from the first collisiondetermining algorithm units on the first stage and the second stage IA,IB. In FIG. 7, other components are identical with those of FIG. 2 sothat the same components are designated by the same reference numerals,and the descriptions thereof are omitted.

In the first collision determining algorithm unit on the first stage IA,a threshold value g_(a) of the subtraction processing portion 2a is setto output the starting signal by even the low speed collision so as toavoid bombing by mistake. In the first collision determining algorithmunit on the second stage IB, the constant value g_(b) of the subtractionprocessing portion 3a and the threshold value v_(b) of the comparisonprocessing portion 3c are set so as to output the starting signal inresponse to the high speed collision. Further, the AND circuit 6 obtainsthe AND of the outputs from both the collision determining algorithmunits IA, IB. Therefore, the second collision determining algorithm unitII can serve as a high speed collision determining algorithm unit havinga malfunction preventing function.

A description will now be given of the operation of the embodiment ofFIG. 7 with reference to a flowchart of FIG. 8. A sampling time is inputin Step ST47, the offset values g_(a), g_(b) of the acceleration areinput in Step ST48, and the threshold values v_(a), v_(b) for use incollision determination are input in Step ST49. In Step ST50, theacceleration preceding by one moment is initialized to zero, and in StepST51, the integrated value is initialized to zero. In Step ST52, theacceleration signal from the G sensor 1 is input into A, and theoperation proceeds to a sub-flowchart 1 shown in FIG. 9 in Step ST53.

Subsequently, the process from Step ST63 to Step ST68 shown in FIG. 9 isperformed as in the case of that from Steps ST37 to ST42 of FIG. 5.However,.the operation proceeds from Step ST 67 in the direction of NOto Step ST69 so as to return to Step ST54 of FIG. 8. In Step ST54, if itis determined that a predetermined time period has elapsed since asignal of High was obtained in step ST68, the operation proceeds to StepST55 where a signal V_(a) is set to Low. Next, the operation proceeds tosub-flowchart 2 in Step ST56 so as to perform the process from StepsST70 to ST77 shown in FIG. 9 as in the case of the sub-flowchart 1.Thereafter, the operation returns to Step ST57. In Step ST57, if it isdetermined that a predetermined time period has elapsed since a proceedsto Step ST59 where V_(a) and V_(b) are ANDed. If the signal V_(b) becameHigh, the operation proceeds to Step ST58 where the signal V_(b) is setto Low. Further, the operation result is Low, the operation returns toStep ST52 so as to repeat the above-mentioned process. Otherwise, if theresult is High, the starting signal is output in Step ST60, and theprocess is terminated in Step ST61.

Embodiment 3

FIG. 10 is a block diagram showing one embodiment according to the thirdaspect of the present invention.

In FIG. 10, reference numeral III is a third collision determiningalgorithm unit. The third collision determining algorithm unit IIIincludes a band pass filter 4a at an input terminal of the firstcollision determining algorithm unit I, and is processed by amicrocomputer.

A description will now be given of the process with reference to aflowchart shown in FIG. 11. The process from Steps ST79 to ST91 in FIG.11 is performed as in the case of that from Steps ST32 to ST43 of FIG. 4except that the acceleration signal passes through the band pass filter4a so as to limit band in Step ST83. The process is terminated in StepST92.

In Step ST83, characteristic of the band pass filter 4a is determined asfollows: In FIG. 12, (a) shows a frequency spectrum of the collisionsignal at the time of typical intermediate and high speed travelling,(b) shows frequency spectrum of the collision signal in the specialcollision (such as slipping under a rear deck of a truck), and (c) showsa filter characteristic in case the band pass filter 4a is provided bydefining cut off frequencies f_(CL), f_(CH) in a frequency banddepending upon (a) and (b), in which a characteristic of the specialcollision is obvious.

A description will now be given of an actual effect of the filter in theacceleration waveform.

In FIG. 13, (A) shows an acceleration signal waveform in a low speedhead-on collision which requires no starting signal, and an accelerationsignal waveform at the time of a high speed special collision whichrequires the starting signal. In FIG. 13, (B) shows a waveform afterpassing an original signal through the band pass filter 4a, (C) shows awaveform obtained by integrating after subtracting a constant value gfrom the original signal, and (D) shows a waveform when subtracting apredetermined acceleration from the waveform (B) and thereafterintegrating after passing through the band pass filter.

As shown in FIG. 13, the constant value g is subtracted from theacceleration signal generated in the low speed head-on collision whichrequires no starting signal, and the subtracted acceleration signal isintegrated so as to define a threshold value V_(TH) which is greaterthan the integrated value. A desired sensing time point required forprotecting a passenger is defined as t₁, and the waveform obtained byintegrating after subtracting the constant value g from the accelerationsignal at the time of, the high speed special collision can reach thethreshold value V_(TH) at a time point t₂. However, the time point t₂exceeds the desired sensing time point t₁ so that sufficient protectionto the passenger can not be provided by the starting signal at the timepoint t₂.

A predetermined value g' is subtracted from the original signal, and isintegrated after passing the original signal through the band passfilter 4a, resulting in a waveform of low speed head-on collision shownin FIG. 13(D). Accordingly, a threshold value can be set less than thethreshold value V_(TH) can be set by defining threshold value V_(TH) 'depending upon the resulting waveform. A time point t₃ serves as a timepoint when the waveform at the time of the high speed special collisionreaches the threshold value V_(TH) ', and the time point t₃ is less thanthe desired sensing time point t₁. As a result, it is possible tosufficiently protect the passenger by using the starting signal at thetime point t₃.

However, there are some drawbacks in the acceleration signal at the timeof the high speed rough road travelling at which the starting signalshould not be output. That is, in the acceleration signal, there aremany frequency components identical with those at the time of high speedspecial collision, and a larger signal remains even after passingthrough the band pass filter. Further, the integrated value of theacceleration signal may reach the threshold value V_(TH) ' as in thecase of the high speed special collision.

Hence, a description will be later given of a discrimination method thehigh speed rough road travelling by using a large negative accelerationsignal which is also generated at the time of the high speed rough roadtravelling with reference to FIG. 13. However, preceding to thedescription, another description will now be given of a startingapparatus employing a fourth collision determining algorithm unit IVcontained in the algorithm with reference to FIG. 14.

Embodiment 4

FIG. 14 is a block diagram showing one embodiment according to thefourth aspect of the present invention. In FIG. 14, a fourth collisiondetermining algorithm unit IV includes a positive acceleration signalpassing means 5a, and a negative acceleration signal inverting/passingmeans 5b at the input terminals of the first collision determiningalgorithm units on the first stage IA and the second stage IB. Further,the fourth collision determining algorithm unit IV includes an ANDcircuit 93 which obtains the AND of outputs from both the firstcollision determining algorithm units IA, IB.

The starting apparatus of the embodiment processes the accelerationsignals fed from the G sensor 1 on the positive side and on the negativeside, separately. That is, the acceleration signal on the positive sideis output from the positive acceleration signal passing means 5a, and isdetermined by the first collision determining algorithm unit IA so as tooutput the starting signal. Similarly, the acceleration signal on thenegative side is inverted and output by the negative acceleration signalinverting/passing means 5b, and is determined by the first collisiondetermining algorithm unit IB so as to output the starting signal.Finally, in the AND circuit 93, both the outputs to actuate startingmeans 28 are ANDed.

A description will now be given of the operation of the fourth collisiondetermining algorithm unit IV with reference to a flowchart shown inFIG. 15. First, in Step ST95, a sampling time T is input, and a lowspeed offset acceleration g_(d) and an intermediate and high speedoffset acceleration g_(e) are input. In Step ST96, output of thestarting signal is stopped. The value B₋₁ of acceleration preceding byone moment and the integrated value F are respectively set to zero inStep ST97, and a value B₋₁ ' of acceleration preceding by one moment andthe integrated value F' are respectively set to zero in Step ST98. InStep ST99, the acceleration signal is fetched into A.

In case a value A is greater than zero in Step ST100, the operationproceeds to Step ST101 to subtract the offset value from A, and proceedsto Step ST102 where trapezoidal integration is performed. In Step ST105,a current value of B is set to the value B₋₁ of acceleration precedingby one moment. In Step ST104, if the integrated value F is less thanzero, the operation proceeds to Step ST105 where the integrated value Fis clamped to zero, and proceeds to Step ST106. In Step ST104, if theintegrated value F is greater than zero, the operation proceeds to StepST106 so as to compare the integrated value F with the threshold valueV_(TH). In Step ST106, the integrated value F is greater than thethreshold value V_(TH), the operation proceeds to Step ST107 where thestarting signal is output.

In Step ST106, if the integrated value F is less than the thresholdvalue V_(TH), the operation proceeds to Step ST99 so as to repeat theprocess set forth above. In Step ST100, if the value A is less thanzero, the process from Steps ST109 to ST114 is performed as in the caseof that from Steps ST101 to ST106. In Step ST114, if the integratedvalue F' is greater than the threshold value V_(TH) ', the operationproceeds to Step ST115 where the integrated value F is reset to zero.

Embodiment 5

FIG. 16 is a block diagram showing one embodiment according to the fifthaspect of the present invention. In FIG. 16, reference numeral V means afifth collision determining algorithm unit. The fifth collisiondetermining algorithm unit V includes the third collision determiningalgorithm unit III shown in FIG. 10, the fourth collision determiningalgorithm unit IV shown in FIG. 14, an AND circuit 9 obtaining the ANDof outputs from both the collision determining algorithm units III andIV, and switching means 10 for opening and closing an input route of thefourth collision determining algorithm unit IV.

A description will now be given of the operation of the fifth collisiondetermining algorithm unit V with reference to a flowchart of FIG. 17.First, output of the starting signal is stopped in Step 117, and theflowchart 3 of FIG. 1 is performed in Step ST118 and the flowchart 4 ofFIG. 15 is performed in Step ST119. In Step ST120, outputs in StepsST118 and ST119 are ANDed. If the AND is High, the operation proceeds toStep ST121 where the starting signal is output. Otherwise, if the AND isLow, the operation returns to Step ST118 so as to repeat the process setforth above.

However, when the flowchart 3 is performed in Step ST118, the operationjumps from Step ST90 of FIG. 11 to Step ST92 without outputting thestarting signal in Step ST91, instead of proceeding from Step ST90 inthe direction of NO. Similarly, in the flowchart 4 in Step ST119, theoperation jumps from Steps ST106 and ST114 of FIG. 15 to Step ST108 soas to return to Step ST120, instead of proceeding in the direction of N.

FIG. 18 is signal waveform diagrams illustrating the operation of thefifth collision determining algorithm unit V. If an accelerationwaveform as shown in FIG. 18 (A) is obtained, the signal passes throughthe band pass filter 4a in the third collision determining algorithmunit III, resulting in a waveform as shown in FIG. 18 (B). If apredetermined acceleration is subtracted from the signal and thesubtracted signal is integrated, a waveform as shown in FIG. 18(C) canbe provided. In this case, the integrated value reaches the thresholdvalue v_(e) at a time point t₁, and a signal is output into an on-timer4e shown in FIG. 26 if the integrated value exceeds the threshold valuev_(e).

Integrating means 5c, 5g are kept in a reset state until the process setforth above is completed. The switch 10 is closed by using the outputsignal from the on-timer 4e as a trigger so as to start the algorithmunit IV. Further, reset states of the integrating means 5c and 5e arereleased, and the acceleration waveform A only on the positive side fora time period from the time points t₁ to t₂ is fetched. The amount ofoffset g_(d) is subtracted from the fetched acceleration waveform A, andthereafter the subtracted acceleration is integrated in the integrationprocessing portion 5c, resulting in a waveform as shown in FIG. 18(D) onthe side of (+). A threshold value v_(d) of a comparison processingportion 5d is set to a value greater than the integrated value, and anoutput from the comparison processing portion 5d is left Low.

For a period from the time points t₂ to t₃, an acceleration of theacceleration waveform (A) on the negative side is inverted and detected.The amount of offset g_(e) is subtracted from the detected acceleration,and thereafter the subtracted acceleration is integrated in theintegration processing portion 5g. If the integrated accelerationexceeds the starting level v_(e), the comparison processing portion 5houtputs High, and the result of OR process 11 is High. As a result, thecomparing means 5d outputs Low since the integrating means 5c is reset.

Finally, in the AND circuit 9, the output from the comparing means 5d isANDed with the output from the third collision determining algorithmunit III so that the starting signal is not input into an on-timer 4f.As a result, it is possible to avoid a malfunction at the time of therough road travelling having a large acceleration signal on the negativeside.

As set forth hereinbefore, in the AND circuit 9, the output from thethird collision determining algorithm unit III is ANDed with the outputfrom the fourth collision determining algorithm unit IV so as to use theAND as a new starting signal.

Embodiment 6

FIG. 19 is a block diagram showing one embodiment according to the sixthaspect of the present invention. In FIG. 19, reference numeral VI meansa sixth collision determining algorithm unit. The sixth collisiondetermining algorithm unit VI is provided by adding the first collisiondetermining algorithm unit I shown in FIG. 2 to the fifth collisiondetermining algorithm unit V shown in FIG. 16 as mistake bombingavoiding means. Further, the sixth collision determining algorithm unitVI is further provided with an AND circuit 8 obtaining the AND of theoutputs from both the collision determining algorithm units V and I, andis processed by the microcomputer shown in FIG. 3.

A description will now be given of the operation of the sixth collisiondetermining algorithm unit VI with reference to a flowchart of FIG. 20.The output of the starting signal is stopped in Step ST124, and theoperation proceeds from Step ST125 to the flowchart 1a shown in FIG. 4.The offset acceleration g_(a) is input in Step ST131 of FIG. 21, and thevalue B₋₁ of the acceleration preceding by one moment and the integratedvalue F are initialized to zero in Step ST132. The offset value g_(a) issubtracted from A in Step ST133, and the trapezoidal integration isperformed in Step ST134. Current acceleration B is input intoacceleration preceding by one moment in Step ST135, and the operationproceeds to Step ST138 if the integrated value F is less than zero inStep ST136. In Step ST138, if the integrated value F is greater than thethreshold value v_(a), the operation proceeds to Step ST139 where thethreshold value v_(a) is set to High. Otherwise, the operation proceedsto Step ST140 so as to return to the flowchart 5 in Step ST126.

Subsequently, the flowchart 5 is performed in Step ST126, and theoperation proceeds to Step ST127 where outputs v_(a) and V_(f) from theSteps ST125 and ST126 are ANDed. If the AND is High, the starting signalis output in Step ST128. If the AND is Low, the operation returns toStep ST125 so as to repeat the process set forth above.

However, in the operation of the flowchart 5 (see FIG. 17) in StepST126, if the AND is Low when V_(c) and V_(d) are ANDed in Step ST120 ofFIG. 17, the operation jumps to Step ST122 instead of outputting thestarting signal in Step ST121. The sixth collision determining algorithmunit VI can discriminate between the rough road travelling and thespecial collision, and includes additional means for preventing frombombing by mistake. As a result, it is possible to perform a highlyreliable determination.

Embodiment 7

FIG. 22 is a block diagram showing one embodiment according to theseventh aspect of the present invention. In FIG. 22 reference numeralVII means a seventh collision determining algorithm unit. The seventhcollision determining algorithm unit VII is provided by adding the firstcollision determining algorithm unit I to the fourth collisiondetermining algorithm unit IV as mistake bombing avoiding means.Further, the seventh collision determining algorithm unit VII isprovided with an AND circuit 95 obtaining the AND of the outputs fromboth the collision determining algorithm units IV and I.

A description will now be given of the operation of the seventhcollision determining algorithm unit VII with reference to FIG. 23. Theoutput of the starting signal is stopped in Step ST149. The operationproceeds to Step ST150 to perform the flowchart 1a (see FIG. 4), and toStep ST151 to perform the flowchart 4 (see FIG. 15). In Step ST152,outputs v_(a) and V_(d) from Steps ST150 and ST151 are ANDed. If theresult is High, the operation proceeds to Step ST153 where the startingsignal is output. If the result is Low, the operation returns to StepST150 so as to repeat the process set forth above.

However, when the operation proceeds to the flowchart 4 in Step ST151 inthe flowchart 7 of FIG. 23, the operation jumps to Step ST108 if F isless than V_(TH) in Step ST106 of FIG. 15. Further, the operation jumpsto Step ST108 to end, instead of outputting the starting signal in StepST107 in case F' is similarly less than V_(TH) ' in Step ST114 and whenthe process in Step ST115 is terminated.

As set forth above, the algorithm for detecting the rough roadtravelling is provided with the mistake bombing avoiding means. As aresult, it is possible to perform a highly reliable determination.

Embodiment 8

FIG. 24 is a block diagram showing one embodiment according to theeighth aspect of the present invention. In FIG. 24, reference numeralVIII means an eighth collision determining algorithm unit. The eighthcollision determining algorithm unit VIII includes the second collisiondetermining algorithm unit II and the sixth collision determiningalgorithm unit VI, and an AND circuit 7 obtaining the AND of the outputsfrom both the collision determining algorithm units II and VI.

A description will now be given of the operation of the eighth collisiondetermining algorithm unit VIII with reference to a flowchart of FIG.25. First, the output of the starting signal is stopped in Step ST142.The operation proceeds to Step ST143 to perform the flowchart 2 (seeFIG. 8), and to Step ST144 to perform the flowchart 6 (see FIG. 20). InStep ST145, outputs V_(h) and V_(g) from Steps ST143 and ST144 areANDed. If the result is High, the operation proceeds to Step ST146 wherethe starting signal is output. If the result is Low, the operationreturns to Step ST143 so as to repeat the process set forth above.

However, when the operation proceeds to the starting signal is output ifthe AND of V_(a) and V_(b) is Low flowchart 2 in Step ST143, theoperation jumps to Step ST61 instead of proceeding to Step ST60 wherethe in Step ST59 of the flowchart 2. Further, when the operationproceeds to the flowchart 6 in Step ST144, the of V_(a) and V_(f) is Lowin Step ST127. In the eighth operation jumps to Step ST129, instead ofproceeding to Step ST128 where the starting signal is output if the ANDcollision determining algorithm unit. VIII, it is possible to perform asynthetic determination of the high speed collision, the low speedcollision, the rough road travelling and the special collision, andthereby output the starting signal.

FIG. 26 is a block diagram showing in detail the eighth collisiondetermining algorithm unit VIII including the first, second, third andfourth collision determining algorithm units I, II, III and IV shown inFIGS. 2, 7, 10, and 14. In FIG. 26, components identical with those inthe respective drawings are designated by the same reference numerals,and the descriptions thereof are omitted.

FIG. 27 is a flowchart illustrating the operation of the eighthcollision determining algorithm unit VIII shown in FIG. 26. Referringnow to FIG. 27, the output of the starting signal is stopped in StepST12, and the operation proceeds to Step ST13 to perform the algorithmI, to Step ST14 to perform the algorithm I', to Step ST15 to perform thealgorithm III, and to Step ST16 to perform the algorithm IV. In StepST17, the output V_(a) in ST13 and the output V_(d) in ST14 are ANDedand the result is defined as Vh. Further, in Step ST18, the output V_(c)in ST15 and output V_(d) in ST16 are ANDed and the result is defined asV_(f). A High state of V_(r) is held for a predetermined period in StepST19, and V_(a) and V_(f) are ANDed in Step ST20 and the result isdefined as V_(g). In Step ST21, V_(h) and V_(g) are ANDed and the resultis defined as V_(i). In Step ST22, if the value V_(i) is High, theoperation proceeds to Step ST23 so as to output the starting signal, andproceeds to Step ST24 to end. If V_(i) is Low, the operation returns toStep ST13 so as to repeat the process set forth above.

Though the collision determining units in the embodiments are processedby a software in the microcomputer, the collision determining unit maybe partially or completely provided to include only hardware circuits.

As set forth above, according to the first aspect of the presentinvention, there is provided the first collision determining algorithmunit to perform an integration with the speed signal defined as zero incase the speed signal obtained by integrating after subtracting theconstant value from the acceleration signal is less than zero. As aresult, there are advantages of reduction of the collision determiningtime, as well as removal of a trigger circuit for resetting theintegration circuit.

According to the second aspect of the present invention, there isprovided the second collision determining algorithm unit including thefirst collision determining algorithm unit on the first stage whichoutputs in response to even a relatively soft collision, the firstcollision determining algorithm unit on the second stage which outputsin response to the high speed collision, and the AND circuit whichobtains the AND of outputs from both the first collision determiningalgorithm units. As a result, there is an effect in that furtheraccurate determination can be performed at the time of the high speedcollision.

According to the third aspect of the present invention, there isprovided the third collision determining algorithm unit employing theband pass filter on the preceding stage of the first collisiondetermining algorithm unit. As a result, there is an effect in that itis possible to extract the characteristics of the acceleration signalwaveforms of the low speed head-on collision and the high speed head-oncollision so as to discriminate therebetween.

According to the fourth aspect of the present invention, there isprovided the fourth collision determining algorithm unit for comparingan output of the integrated acceleration signal on the positive sidewith an output of the integrated acceleration signal on the negativeside in the acceleration signals so as to define a more rapidly outputas the starting signal. As a result, there is an effect in that therough road travelling can be discriminated since an acceleration signalwaveform is also formed largely on the negative side at the time of therough road travelling.

According to the fifth aspect of the present invention, there isprovided the fifth collision determining algorithm unit which is acombination of the third collision determining algorithm unit and thefourth collision determining algorithm unit. As a result, there is aneffect in that a highly reliable discrimination can be performed betweenthe rough road travelling and the special collision.

According to the sixth aspect of the present invention, there isprovided the sixth collision determining algorithm unit which is acombination of the first collision determining algorithm unit and thefifth collision determining algorithm unit. As a result, there areeffects in that a safety function can be provided, and a highly reliablediscrimination can be performed between the rough road travelling andthe special collision.

According to the seventh aspect of the present invention, there isprovided the seventh collision determining algorithm unit which is acombination of the first collision determining algorithm unit and thefourth collision determining algorithm unit. As a result, there areeffects in that a safety function can be provided, and a highly reliablediscrimination of the rough road travelling can be performed.

According to the eighth aspect of the present invention, there isprovided the eighth collision determining algorithm unit which is acombination of the second collision determining algorithm unit and thesixth collision determining algorithm unit. As a result, There is aneffect in that a highly reliable discrimination can be performed betweenthe high speed collision and the rough road travelling and the specialcollision among all the collisions.

While preferred embodiments of the invention have been described usingspecific terms, such description is for illustrative purposes only, andit is to be understood that changes and variations may be made withoutdeparting from the spirit or scope of the following claims.

What is claimed is:
 1. A starting apparatus of a passenger protectingapparatus comprising:an acceleration sensor converting an accelerationat a time of collision into an acceleration signal; subtracting meansfor subtracting a predetermined offset value from said accelerationsignal output from said acceleration sensor; speed calculating means forintegrating output from said subtracting means so as to obtain a speedsignal; limiting means for limiting said speed signal to zero when anintegrated value of said output from said subtracting means becomessmaller than zero; comparing means for comparing an output from saidspeed calculating means with a threshold value; and starting means foroutputting a starting signal depending upon an output from saidcomparing means.
 2. A starting apparatus of a passenger protectingapparatus comprising:an acceleration sensor converting an accelerationat a time of collision into an acceleration signal; a low speeddetermining portion having,first subtracting means for subtracting afirst predetermined offset value from said acceleration signal outputfrom said acceleration sensor, first speed calculating means forintegrating an output from said first subtracting means so as to obtaina first speed signal, and first comparing means for comparing an outputfrom said first speed calculating means with a first threshold value,and first limiting means for limiting said first speed signal to zerowhen an integrated value of said output from said first subtractingmeans becomes smaller than zero; a high speed determining portionhaving,second subtracting means for subtracting a second predeterminedoffset value from said acceleration signal output from said accelerationsensor, second speed calculating means for integrating an output fromsaid second subtracting means so as to obtain a second speed signal, andsecond comparing means for comparing an output from said second speedcalculating means with a second threshold value larger than said firstthreshold value, and second limiting means for limiting said secondspeed signal to zero when an integrated value of said output from saidsecond subtracting means becomes smaller than zero; an AND circuitobtaining an AND of an output from said low speed determining portionand an output from said high speed determining portion; and startingmeans for outputting a starting signal depending upon an output fromsaid AND circuit.
 3. A starting apparatus of a passenger protectingapparatus according to claim 2, wherein said first predetermined offsetvalue is smaller than said predetermined offset value.
 4. A startingapparatus of a passenger protecting apparatus according to claim 2,wherein said first threshold value is smaller than said second thresholdvalue.
 5. A starting apparatus of a passenger protecting apparatuscomprising:an acceleration sensor converting an acceleration at a timeof collision into an acceleration signal; a filter allowing onlyparticular frequencies in acceleration signals output from saidacceleration sensor to pass; subtracting means for subtracting apredetermined offset value from an output from said filter;speedcalculating means for integrating an output from said subtracting meansso as to obtain a speed signal; limiting means for limiting said speedsignal to zero when an integrated value of said output from saidsubtracting means becomes smaller than zero; comparing means forcomparing an output from said speed calculating means with a thresholdvalue; and starting means for outputting a starting signal dependingupon an output from said comparing means.
 6. A starting apparatus of apassenger protecting apparatus according to claim 5, wherein:said filtercuts frequencies peculiar to a collision against a rear end of a truck.7. A starting apparatus of a passenger protecting apparatus according toclaim 1, further comprising:holding means for maintaining said startingsignal for a predetermined length of time.
 8. A starting apparatus of apassenger protecting apparatus according to claim 1, wherein,saidpredetermined offset value is set at a value where the output of saidsubtracting means is a negative value when a vehicle is running at a lowspeed and starting of said passenger protecting apparatus is notnecessary.
 9. A starting apparatus of a passenger protecting apparatus,comprising:an acceleration sensor converting an acceleration at a timeof collision into an acceleration signal; a subtractor subtracting apredetermined offset value from the acceleration signal output from saidacceleration sensor; an integrator integrating output from saidsubtractor to obtain a speed signal; a limiter limiting said speedsignal to zero when an integrated value of said output from saidsubtractor becomes smaller than zero; a comparator comparing an outputfrom either one of said integrator or said limiter with a thresholdvalue; and a starter outputting a starting signal based on an outputfrom said comparator.
 10. A starting apparatus of a passenger protectingapparatus according to claim 9, further comprising:a timer maintainingsaid starting signal for a predetermined length of time.
 11. A startingapparatus of a passenger protecting apparatus according to claim 9,wherein,said predetermined offset value is set at a value where saidoutput of said subtractor is a negative value when a vehicle is runningat a low speed and starting of said passenger protecting apparatus isnot necessary.
 12. A method for starting a passenger protectingapparatus, comprising the steps of:(a) detecting an amount ofacceleration applied to a vehicle; (b) subtracting a predeterminedoffset value from said amount of acceleration detected in said step (a)to obtain a subtracted value; (c) integrating said subtracted valuecalculated in said step (b) to obtain a speed signal; (d) limiting saidspeed signal to zero when an integrated value of said subtracted valuebecomes smaller than zero; (e) comparing said speed signal with athreshold value; and (f) generating a starting signal for starting saidpassenger protecting apparatus according to the comparison result insaid step (e).
 13. The method for starting a passenger protectingapparatus according to claim 12, further comprising the step of:(g)maintaining said start signal for a predetermined period of time. 14.The method for starting a passenger protecting apparatus according toclaim 12, wherein,said predetermined offset value is set at a value suchthat said subtracted value is a negative value when a vehicle is runningat a low speed and starting of said passenger protecting apparatus isnot necessary.
 15. A starting apparatus of a passenger protectingapparatus comprising:an acceleration sensor converting an accelerationat a time of collision into an acceleration signal; a first subtractorsubtracting a first predetermined offset value from said accelerationsignal output from said acceleration sensor; a first integratorintegrating output from said first subtractor to obtain a first speedsignal; a first limiter limiting said first speed signal to zero when anintegrated value of said output from said first subtractor becomessmaller than zero; a first comparator comparing an output from eitherone of said first integrator or said first limiter with a firstthreshold value; a first starter outputting a first starting signalbased on an output from said first comparator; a second subtractorsubtracting a second predetermined offset value from said accelerationsignal output from said acceleration sensor; a second integratorintegrating output from said second subtractor to obtain a second speedsignal; a second limiter limiting said second speed signal to zero whenan integrated value of said output from said second subtractor becomessmaller than zero; a second comparator comparing an output from eitherone of said second integrator or said second limiter with a secondthreshold value; a second starter outputting a second signal based on anoutput from said second comparator; and a third starter outputting athird starting signal to start said passenger protecting apparatus whensaid first starting signal and said second starting signal are bothoutputted.
 16. A starting apparatus of a passenger protecting apparatusaccording to claim 15, wherein:said third starting signal is outputtedwhen both said first starting signal and said second starting signal areoutputted within a predetermined period of time.
 17. A startingapparatus of a passenger protecting apparatus according to claim 15,wherein:said first starting signal is indicative of a low speedcollision, and said second starting signal is indicative of a high speedcollision.
 18. A starting apparatus of a passenger protecting apparatusaccording to claim 15, wherein said third starter comprises:an ANDcircuit for receiving said first starting signal and said secondstarting signal and outputting said third starting signal.
 19. A methodfor starting a passenger protecting apparatus, comprising the stepsof:(a) detecting an amount of acceleration applied to a vehicle; (b)subtracting a first predetermined offset value from said amount ofacceleration detected in said step (a) to obtain a first subtractedvalue; (c) integrating said first subtracted value calculated in saidstep (b) to obtain a first speed signal; (d) limiting said first speedsignal to zero when an integrated value of said first subtracted valuebecomes smaller than zero; (e) comparing said first speed signal with afirst threshold value; and (f) generating a first starting signalaccording to the comparison result in said step (e); (g) subtracting asecond predetermined offset value from said amount of accelerationdetected in said step (a) to obtain a second subtracted value; (h)integrating said second subtracted value calculated in said step (g) toobtain a second speed signal; (i) limiting said second speed signal tozero when an integrated value of said second subtracted value becomessmaller than zero; (j) comparing said second speed signal with a secondthreshold value; and (k) generating a second starting signal accordingto the comparison result in said step (j); (l) generating a thirdstarting signal for starting said passenger protecting apparatus whenboth said first starting signal and said second starting signal aregenerated.
 20. The method for starting a passenger protecting apparatusaccording to claim 19, wherein:said third starting signal is generatedwhen both said first starting signal and said second starting signal aregenerated within a predetermined period of time.
 21. The method forstarting a passenger protecting apparatus according to claim 19,wherein:said first starting signal is indicative of a low speedcollision, and said second starting signal is indicative of a high speedcollision.
 22. A starting apparatus of a passenger protecting apparatusaccording to claim 5, wherein:said predetermined offset value is set ata value where said output of said subtracting means is a negative valuewhen a vehicle is running at a low speed and starting of said passengerprotecting apparatus is not necessary.
 23. A starting apparatus of apassenger protecting apparatus, comprising:an acceleration sensorconverting an acceleration at a time of collision into an accelerationsignal; a filter allowing only particular frequencies in saidacceleration signals output from said acceleration sensor; a subtractorsubtracting a predetermined offset value from said acceleration signaloutput from said acceleration sensor; an integrator integrating outputfrom said subtractor to obtain a speed signal; a limiter limiting saidspeed signal to zero when an integrated value of said output subtractorbecomes smaller than zero; a comparator comparing an output from eitherone of said integrator or said limiter with a threshold value; and astarter outputting a starting signal based on an output from saidcomparator.
 24. A starting apparatus of a passenger protecting apparatusaccording to claim 23, wherein:said predetermined offset value is set ata value where an output of said subtractor is a negative value when avehicle is running at a low speed and starting of said passengerprotecting apparatus is not necessary.
 25. A starting apparatus of apassenger protecting apparatus according to claim 23, wherein:saidfilter cuts frequencies peculiar to a collision against a rear end of atruck.
 26. A method for starting a passenger protecting apparatus,comprising the steps of:(a) detecting an amount of acceleration appliedto a vehicle; (b) filtering said amount of acceleration detected by saidstep (a) to pass only particular frequencies; (c) subtracting apredetermined offset value from said amount of acceleration detected insaid step (a) and filtered in said step (b) to obtain a subtractedvalue; (d) integrating said subtracted value calculated in said step (c)to obtain a speed signal; (e) limiting said speed signal to zero when anintegrated value of said subtracted value becomes smaller than zero; (f)comparing said speed signal with a threshold value; and (g) generating astarting signal for starting said passenger protecting apparatusaccording to the comparison result in said step (f).
 27. The method forstarting a passenger protecting apparatus according to claim 26,wherein,said predetermined offset value is set at a value such that saidsubtracted value is a negative value when a vehicle is running at a lowspeed and starting of said passenger protecting apparatus is notnecessary.
 28. The method for starting a passenger protecting apparatusaccording to claim 26, wherein,frequencies peculiar to a collisionagainst a rear end of a truck are cut in said step (b).